Diastereoselective synthesis of psi[(E)-CH=CMe]- and psi[(Z)-CH=CMe]-type dipeptide isosteres by organocopper-mediated anti-S(N)2' reaction

[reaction: see text] Acyclic psi[(E)-CH=CMe]- and psi[(Z)-CH=CMe]-type dipeptide isosteres were efficiently synthesized. In a key reaction, alpha-alkylation of gamma-mesyloxy-beta-methyl-alpha,beta-unsaturated esters with organocyanocuprates in diethyl ether or tetrahydrofuran preferentially afforded the psi[(E)-CH=CMe]- or psi[(Z)-CH=CMe]-isomer, respectively, via anti-S(N)2' mechanism.     

Dehydration reactions in water. Brønsted Acid-surfactant-combined catalyst for ester,ether, thioether,and dithioacetal formation in water

Dehydration reactions in water have been realized by a surfactant-type catalyst, dodecylbenzenesulfonic acid (DBSA). These reactions include dehydrative esterification, etherification, thioetherification, and dithioacetalization. In these reactions, DBSA and substrates form emulsion droplets whose interior is hydrophobic enough to exclude water molecules generated during the reactions. Detailed studies on the esterification revealed that the yields of esters were affected by temperature, amounts of DBSA used, and the substrates. Esters were obtained in high yields for highly hydrophobic substrates. On the basis of the difference in hydrophobicity of the substrates, unique selective esterification and etherification in water were attained. Furthermore, chemospecific, three-component reactions under DBSA-catalyzed conditions were also found to proceed smoothly. This work not only may lead to environmentally benign systems but also will provide a new aspect of organic chemistry in water.     

Reaction of enaminones with carbon disulfide: Synthesis of heterocycles using enamino dithiocarboxylates

Reaction of various types of enaminones, which are prepared by the condensation of 1,3-dicarbonyl compounds with aromatic amines, with carbon disulfide in the presence of sodium hydroxide as the base in dimethyl sulfoxide to give the corresponding enamino dithiocarboxylates, 1,3-thiazines and trithiones. Enamino dithiocarboxylates are cyclized under refluxing in diphenyl ether to give the fused quinoline derivatives. The reaction of 6-arylamino-1,3-dimethyluracils with excess carbon disulfide in the presence of sodium hydroxide and subsequent methylation with dimethyl sulfate gave directly the corresponding 1,3-dimethyl-5-methylthiopyrimido[4,5-b]quinoline-2,4(1H,3H)-diones.     

Amidase and peptidase activities of polyclonal immunoglobulin G present in the sera of patients with rheumatoid arthritis

Polyclonal Immunoglobulin (Ig) G from patients with rheumatoid arthritis (RA) and healthy subjects hydrolyzed carbobenzoxy−Val−Gly−Arg p-nitroanilide and D−Pro−Phe−Arg p-nitroanilide. RA IgG exhibited higher activity against the former substrate, but not the latter. On the other hand, RA IgG showed reduced activity against D−Pro−Phe−Arg methylcoumarinamide, when compared with those of the healthy controls. These results suggest that RA IgGs differ from normal IgGs in the substrate specificity of amidase activity. Preliminary studies have shown that two out of three RA IgG samples cleaved a pentapeptide—Gln−Arg−Arg−Arg−Ala−Ala— which is assumed to be associated with the risk of developing RA (Gregersen, P. K. et al. (1987), Arthritis Rheum. 30, 1205–1213). By contrast, virtually no cleavage of the same peptide was observed with IgG from healthy controls. A peptide analog, Gln−Arg−Arg−Trp−Ala, was not cleaved at all by any IgGs examined either from RA patients or healthy controls.     

Dimethylsilyl ketene acetal as a nucleophile in asymmetric Michael reaction: enhanced enantioselectivity in oxazaborolidinone-catalyzed reaction

[reaction: see text] Dimethylsilanyl [Me2Si(H)] ketene S,O-acetal 6b is an effective nucleophile that retards the undesirable Si+-catalyzed racemic pathway in the oxazaborolidinone-catalyzed asymmetric Michael reaction. Through the further suppression of the Si+-catalyzed pathway by carrying out the reaction in the presence of 2,6-diisopropylphenol and t-BuOMe as additives, enantioselectivity up to 98% ee could be achieved for a variety of acyclic enones.     

Synthesis of pyrimidine derivatives using N-bis(methylthio)methylenecyanamide

N-Bis(methylthio)methylenecyanamide ( 1 ) was allowed to react with active methylene compounds (methyl cyanoacetate, dimethyl malonate, ethyl acetoacetate, ethyl phenylacetate) in the presence of potassium carbonate or potassium hydroxide in dimethyl sulfoxide followed by the treatment using appropriate a base or an acid to give the corresponding 6-methylthiouracil derivatives in 15–80% yields. These uracil derivatives are found to be useful intermediates for the synthesis of 6-aminouracils and fused pyrimidine derivatives.     

Catalytic asymmetric desymmetrization of cyclic meso-1,3- and 1,4-diols by a phosphinite derivative of quinidine

Asymmetric monobenzoylation reactions of cyclic meso-1,3- and 1,4-diols were catalyzed by a phosphinite derivative of quinidine to afford the corresponding monobenzoylated diol with good yield and enantioselectivity. [reaction: see text]     

Photoinduced electron-transfer systems consisting of electron-donating pyrenes or anthracenes and benzimidazolines for reductive transformation of carbonyl compounds

Photoinduced electron-transfer reactions of several ketone substrates were studied to evaluate the utilities of 1,6-bis(dimethylamino)pyrene (BDMAP), 1,6-dimethoxypyrene (DMP), 9,10-bis(dimethylamino)anthracene (BDMAA), and 9,10-dimethoxyanthracene (DMA) as electron-donating sensitizers cooperating with 2-aryl-1,3-dimethylbenzimidazolines. BDMAP and DMP generally led higher conversion of ketones and better yield of reduction products compared to BDMAA and DMA.     

Isolation of xylose reductase gene ofPichia stipitis and its expression inSaccharomyces cerevisiae

Applied Biochemistry and Biotechnology - A NADPH/NADH-dependent xylose reductase gene was isolated from the xylose-assimilating yeast,Pichia stipitis. DNA sequence analysis showed that the gene...     

Diethyl phosphorocyanidated (DEPC). A novel reagent for the classical Strecker's α-amino nitrile synthesis

Diethyl phosphorocyanidate (DEPC) can be efficiently used for the synthesis of α-amino nitriles from carbonyl compounds and amines. The reaction may be called a modified Strecker synthesis.